The present invention generally relates to telecommunication systems and in particular to a telecommunication system or network that has the capability of transferring a call directed to a terminal to another terminal.
The term "call transfer" used throughout the specification should be understood as call forwarding in a call forwarding system which automatically reroutes a call to be routed to the called station, to an alternate station.
The capability of transferring incoming call from a first destination terminal to a second destination terminal based upon registration in the network is used extensively. According to such a transfer capability, one can receive the call even when working at a location different from the usual working place, without human intervention for transferring the call. On the other hand, there can be an inconvenience in such a system in that the user cannot know whether there occurred a transfer of call in the terminal unless he or she answers the call at the working place to which the call is transferred. When the user is absent and has failed to answer the transferred call, there remains no record, in any of the first terminal to which the call has come in at first and the second terminal to which the call has been transferred from the first terminal, of the fact that there has been an incoming call and the same has been transferred. Thereby, the user cannot know the fact that the transfer of the call has occurred, even when he or she has returned to the usual work place.
FIG. 1 shows the construction of a conventional telecommunication system that has the capability of transferring a call.
Referring to FIG. 1, the telecommunication system includes a switching station 1 having the capability of transferring a call. There, the switching station 1 is connected to other switching stations 2 and 3, and the switching stations 1-3 form a telecommunication network 10. In the illustrated example, a terminal 7 having a dial number DN.sub.17 is connected to the switching station 2, while a terminal 8 having a dial number DN.sub.1 is connected to the switching station 3. Further, a terminal 6 having a dial number DN.sub.16 is connected to the switching station 1.
The switching station 1 includes a central control unit 12 and a main memory 13 that cooperates with the unit 12, wherein the main memory 13 includes therein a memory field 131 for storing subscriber data SD for each of the terminals connected to the switching station 1. The subscriber data SD includes the information about whether the subscriber at the terminal such as the terminal 6 (DN=DN.sub.16) is entitled to use the call-transfer service of the network or not as indicated by a flag T as well as the information about whether the user activates the call-transfer service or not as indicated by a flag t. For example, the flag T is set to the logic value "1" when the subscriber of the terminal contracts with the vendor of the network about the use of the call-transfer service. Similarly, the flag t is set to "1" when the subscriber or user of the terminal activates the call-transfer service.
In addition, the main memory 13 includes a memory field 132 for storing the dial number of destination terminals to which the call is to be transferred. For example, the memory field 132 may store the dial number DN.sub.17 together with a corresponding abbreviated number.
In operation, the user at the terminal connected to the switching station 1 such as the terminal 6 sets the flag t in the memory field 131 to the logic value "1" via the control unit 12. At the same time, the user sets the dial number of the terminal to which the call is to be transferred such as the terminal 7 (DN=DN.sub.17) in the memory field 131 of the main memory 13 in the abbreviated form. Thus, when a call directed to the terminal 6 comes in, for example from a terminal 8 via the switching station 3, the central control unit 12 of the switching station 1 checks for the flags set in the parameters T and t of the terminal 6 and reads out the dial number DN.sub.17 from the memory field 132. Further, the call is transferred from the switching station 1 to the terminal 7 via the switching station 2 based upon the dial number DN.sub.17 thus retrieved.
Obviously, the system of FIG. 1 lacks the capability of informing the transfer of the call to the terminal 6. In other words, the terminal 6 is not activated at all in the foregoing transfer operation, and the user that normally uses the terminal cannot know the fact that a transfer of an incoming call has occurred while he or she has been absent at the location where the terminal 7 is provided. Further, there can occur a problem that all the incoming calls are transferred, in vain, to the terminal 7 when the user at the terminal 6 has inadvertently activated the call transfer service and conducting activity at the site of the terminal 6.